Railway signaling system



D. G. SHIPP RAILWAY SIGNALING SYSTEM Filed Feb. 20, 1947 Feb. 12, 1952 INVEIYTOR.

fiaay/ aldle Sfigp. BY

QM. R kg Patented Feb. 12, 1952 RAILWAY SIGNALING SYSTEM Douglas Goldie Shipp, London, England, assignor, by mesne assignments, to Westinghouse Air Brake Company, a corporation of Pennsylvania Application February 20, 1947, Serial No. 729,824 In Great Britain March 1, 1946 6 Claims. 1

This invention relates to railway signaling systems employing alternating currenttrack circuits constituted by the track rails divided into sections in which alternating current energy is supplied to the track rails at one end of a track section,

a direct current relay at the other end of the section being arranged to respond to the presence or absence of this energy which is rectified before being applied to the relay.

One of the problems attendant upon all signaling systems employing track circuits is how to guard against failure of the insulated block joints between adjoining sections.

This problem may be solved in systems employing direct current energy applied to the track rails by applying energy of opposite polarities to adjoining sections so that, uponthe failure of a block joint between two sections the relay of one section, which is responsive only to energy of one polarity, will not be operated by energy fed from the adjoining section.

In systems employing alternating current energy and direct current relays, however, the rec'- tiller feeding the relay is equally responsive to an alternating current input of any phase so that the reversal of phase of energy supplied to adjoining track sections is not eifective to give protection against block joint failure. This is par-- naling system embodying my invention and shall ticularly serious in systems where sections are separated by blocks joints in one rail only and in systems where block joints in both rails are employed in conjunction with impedance bonds since in both these cases failure of one block joint may result in false operation of the relay by energize.- tion from an adjoining section.

The object of the present invention is to oversome the above-mentioned difiiculty. To this end,

use is made of phase-sensitive rectification :and according to the principal feature of the invention an alternating current reference voltage-from a local source of supply, which may be the signaling supply lines, is fed into the rectifier :network interposed between the alternating-current supply received from the track rails and the direct current relay.

plied to the relay is in this manner made dependent upon the relative polarities of the two alternating current supplies and the normal technique of arranging for the alternating current energy supplied to adjoining track sections to be of opposite relative polarities and mutually 180 then point out the novel features thereof in claims.

In the drawings,

Fig. 1 is a diagram of a stretch of railway track equipped with track circuits embodying this invention, and

Figs. 2 and 3 are fragmentary views showing modifications which I may employ.

Referring to Fig. 1 of the drawings, there is shown therein a stretch of railway track through which tra-fiic normally moves in the direction indicated by the arrow, that is, from left to right. The track rails l and 2 of the track stretch are divided by insulated joints 3 into the customary track sections for signaling purposes. Two complete track sections, designated BT and CT, and a portion of a third track section, designated AT, are shown in the drawings.

=20 Entrance of trafi'ic into each of the track sections is governed by a signal located at the entrance end of the section and designated S with a prefix corresponding to that of the associated section. As shown, each of the signals is of the -25 color light type and each has a red or stop lamp R,- and green or clear lamp G.

Each of the track sections is provided with track circuit apparatus including a code following track relay at the entrance end of the track section and a supply transformer TT located at the exit end of the track section. The en"rgy supplied from transformer TT is coded or periodically interrupted at a suitable code speed by code The polarity of the direct current :voltageap transmitters designated CT.

- The track relays,'which are designated CFR with a prefix corresponding to that of the associated track section, are of the code following type and control slow releasing code detecting relays FSA and BSA in such manner. that the relay BSA is picked up when and only when the associated track relay is responding to coded energy. The. relays BSA control the lamps of the signalsso that the red .lamp is lighted when the relay BSA is released and the green lamp is lighted when the rela BSA is picked up. 7

The track relays CFR are of the polar biased neutral type and each has a contact which is biased to a released position from which it is moved to a picked-up position when and only when energy of a particularly polarity is supplied to the relay winding, as indicated by the arrow on the relay winding.

The energy supplied to the track rails through the supply transformers is supplied from a suitable central source the terminals of which are aosaaoa designated BX and NX and is distributed throughout the track stretch by a transmission line. The connections between the transmission line and the supply transformers, and between the supply transformers and the track rails, are arranged so that the energy supplied to adjoin ing sectionsis 180 degrees out of phase, that supplied to the one section being of normal relative polarity and that supplied to the other being of the reverse or opposite relative polarity.

Each of the track relays CFR is connected across the track rails through phase sensitive rectifying means which operates as hereinafter explained so that energy effective to pick up the contact of a track relay is supplied to the relay when and only when the energy supplied over the track rails has a predetermined phase relationship such that its relative polarity corresponds to that of the energy supplied locally from the transmission line to the rectifying means.

As shown in Fig. l the relay BCFR has an upper winding Hi, one end terminal of which is connected to one terminal of the condenser BQI and through the asymmetric unit KI to one end terminal of the secondary winding of a track transformer BCTT. The relay BCFR also has a lower winding ll, one end terminal of which is connected to one terminal of the condenser BQZ and through the asymmetric unit K2 to the other end terminal of the secondary winding of transformer BCTT. The other terminals of the windings of relay BCFR are connected to the terminal is intermediate the condensers BQI and BQ2, which terminal is connected to one end terminal of the secondary winding of a line transformer BLT, the other end terminal of which is connected to the center tap I2 on the secondary winding of transformer BGTT. Energy from the transmission line is supplied to the primary winding of transformer BLT, while the secondary winding of'this transformer is provided with taps so that the voltage of the energy supplied therefrom may be adjustably varied as desired. As is hereinafter explained, the equipment is arranged and adjusted so that the relative polarity of the energy from transformer BLT corresponds to that of the energy supplied to the rails of the section by transformer BTT, and its voltage always exceeds that of the energy derived from the rails of the section and supplied from one half of the secondary winding of transformer BCTT. As is apparent, the primary winding of the transformer BCTT is connected across the rails of section BT so as to be supplied with energy from transformer BTT over the track rails.

During the recurring half cycles of the supply voltage when terminal BX is positive with re spect to the terminal NX, the energy supplied to the primary winding of transformer BTT, as-

suming the contact of the code transmitter CT in this circuit is. closed, causes an impulse of energy to be supplied from the transformer secondary winding to the track rails to make track rail 2 positive with respect to track rail I. This energy is supplied over the track rails of section BT, assuming the section to be vacant, to the primary winding of transformer BCT'I and current flows through this winding from its upper to its lower terminal. As a result of this supply of energy through the primary winding of transformer BCTT, there is induced in each of the two track transformer secondary windings l4 and IS an impulse of voltage which is of such polarity as to make the upper end terminal of each winding portion positive with respect to 4 the lower end terminal of the same winding portion.

The impulse of energy induced in the upper portion ll of the secondary winding of transformer BCTT tends to cause current to flow from the upper end terminal of this winding through the asymmetric unit Kl to one terminal of the condenser BQI and the right-hand terminal of the upper winding 10 of relay BCFR, through this winding from right to left to terminal l6 between condensers BQI and BQ2, and thence through the secondary winding of transformer BLT to the center tap l2 on the secondary winding oftransformer BCTT.

The impulse of voltage induced in the lower portion l5 of the secondary winding of the transformer BCTT tends to cause current to flow from terminal 12 through the secondary winding of transformer BLT to terminal I6, and thence through the lower winding H of relay BCFR from right to left, but the how of current of this polarity is blocked by the rectifier K2.

At this time an impulse of voltage is also induced in the secondary winding of transformer BLT and is of such polarity that the left-hand end of the winding is positive with respect to the right-hand end. Accordingly, the voltage induced at this time in the secondary winding of transformer BLT tends to cause current to flow to terminal it, and thence through the lower winding H of relay BCFR from right to left and through the upper winding In of relay BCFR from left to right. However, the rectifiers KI and K2 block the flow of current of this polarity in the circuits of both of the windings of relay BCFR.

Thevarious parts of the equipment are arranged and proportioned so that the impulses induced in the secondary windings of transformers BCTT and BLT are either substantially in phase or degrees out of phase, and so that the voltage of the impulses induced in the secondary winding of transformer BLT exceeds that of the impulses induced in either portion of the secondary winding of the transformer BC'IT.

The voltage induced in the secondary winding of transformer BLT at this time is of the polarity opposite to that induced in the upper portion Id of the secondary winding of transformer BCTT, and as the voltage of the impulse front transformer BLT is assumed to exceed that of? the impulse from the upper portion of the se ondary winding of transformer BCTT, it follows that the resultant voltage is in the direction for'which rectifier Kl blocks the flow of current. In other words, the voltage impulse from transformer BLT supplied to the circuit including the upper winding ID of relay BCFR prevents the voltage impulseinduced in portion Id of the transformer BCTT, from causing the flow of current in the winding in of relay BCFR.

Accordingly,- with the equipment operating as intended, energy is not supplied to either winding of relay BCFR during the half cycles in which terminal BX is positive with respect to terminal NX.

During the recurring half cycles of the supply voltage when terminal NX is positive with respect to terminal BX, the transformer BTT supplies to the track rails an impulse of energy which causes rail I to be positive with respect to rail 2, with the result that energy is supplied to the primary winding of transformer BCTT 3 dausiis t P11l4 1 in each of the p o of the secondary winding of the transformer an impulse of voltage which is of such polarity that the lower end of the winding portion is positive with respect to the upper end of the same portion The voltage impulse induced in the lower portion of the secondary winding of transformer BCTT causes current to flow from the lower end terminal of this winding through rectifier K2 to one terminal of the condenser BQZ, thence through a load or supply circuit comprising the lower winding ll of relay BCFR from left to right to terminal l6, and through the secondary winding of transformer BLT to terminal 12.

The voltage impulse induced in the upper por tion 14 of the secondary winding of transformer BCTT tends to cause current to flow from termi nal l2 through the secondary winding of transformer BLT to terminal 16 and thence through another load of supply circuit comprising the upper winding 10 of relay BCFR but the flow of current of this .polarity is blocked by the rectifier Kl.

At this time an impulse of voltage is induced in the secondary winding of transformer BLT and is of such polarity that the right-hand terminal is positive with respect to the left-hand terminal. Accordingly, current from the sec ondary winding of transformer BLT flows from the right-hand end terminal of the winding to terminal l2, from which it flows through the upper portion H; of the secondary winding of v transformer BCTT, through rectifier Kl, through the upper winding ID of relay BCFR from right to left to terminal I5, and thence to the left hand terminal of the secondary winding of transformer BLT. In addition, current supplied from the secondary winding of transformer BLT flows from the right-hand end terminal of the winding to terminal 12, thence through the lower portion [5 of the secondary winding of transformer BCTT, through the rectifier K2 to the lower terminal of condenser BQZ, and through the lower winding ll of relay BCFR from left to right to terminal l6 and to the left-hand end terminal of the secondary winding of transforme1 BIJT.

From the foregoing it will be seen that during the half cycles in which terminal BX is positive with respect to terminal NX there is no effective flow of energy in either winding of the relay BCFR.

In addition, it will be seen that during the half cycles in which terminal NX is positive with respect to terminal BX the energy impulse suppl ed over the track rails causes transformer BCTT to supply an impulse of current which flows from left to right through the lower winding ll of relay BCFR. In addition, transformer BCTT applies to the circuit of the upper winding of relay BCFR. a voltage which is of such polarity that flow of current through the relay winding due to this voltage is blocked by the rectifier Kl.

Also, during these half cycles, the transformer BLT supplies to the circuits of both windings of the relay BCFR an impulse of voltage of the polarity effective to cause current to flow in the circuit of the relay winding. The current supplied from transformer BLT to the lower wind,- ing !l of relay BCFR supplements or augments that supplied from the lower portion l5 of the secondary winding of transformer BCTT so that the effective energization of winding H of relay BCFR is determined by the sum of the impulses of voltage supplied thereto from transformers stir and BCTT. r V

0n the other hand the efiect .of' the "voltage supplied from transformer BLT to the upper winding H! of relay BCFR is diminished by the opposing voltage supplied to the circuit of this winding by the upper portion IA of the secondary winding of transformer BCTT. As explained above, the voltage supplied from transformer BLT exceeds that .induced in, one half of the secondary winding of transformer BCTT. Accordingly, some current flows in the circuit of the winding H]- of relay BCFR as a result of the impulse of voltage supplied from transformer BLT. i

It will be seen, therefore, that the current supplied to the lower winding ll of relay BCFR is due to the sum of the voltage impulses supplied from transformersBLT and BCTT, while the current suppliedtto the upper winding '19 of relay BCFR is due to the difference between the voltage of the impulses supplied from transformers BLT and BCTT. Accordingly, the current supplied to winding ll substantially exceeds that supplied to winding 10. The current supplied to the upper winding l0 flows therethrough from rightto left, while the current supplied to the lower winding II flows therethrough from left to right, and as the currentsupplied' to winding H exceeds that supplied to winding I the relay BCFR is effectively energized by current flowing from left to right.

The relay BCFR is of the polar biased neutral type, the contacts of which normally occupy a released position from which they are moved to a picked-up position when'and only when current of a selected polarity is supplied to the relay winding. The relay BCFR is connected'in the circuit so that its contacts pick 'up when current flows through the relay winding from-left to right. Accordingly, during the half cycles in which terminal NX is positive with respect to terminal BX energy effective to pick up the contacts of relay BCFR is supplied-to the relay windings and the relay contacts pick up.

The condensers BQI and BQZ are connected in multiplewith windings i0 and l 1, respectively, of relay BCFR so that during the half cycles in which'energy is supplied to the windings of relay BCFR from the transformers a charge proportional to the voltage 'of the energy supplied to the relay windings is built'up'in the condensers, while energy from the condensers flows through the relay winding'sin the half cycles in which energy is not supplied from the transformers. The condensers BQl'and BQZ are of such size that energy supplied therefrom to the windings of relay BCFR maintains the relay contacts picked up during the half cycles in which the transformers BCTT- and BLT do not supply en ergy-to the relay BCFR. The condensers BQ! and BQ2 are also of such size that energy supplied therefrom will not keep the contacts of relay BCFR picked up substantially longer than one half a cycle -of the alternating current source.

'From the foregoing it will be'seen that, when the contactof the code transmitter CT governing the supply of energy to the transformer BTT is closed and, the track section is vacant, the relay BCFR iserierigized from the transformers BLT and BCTT during alternate half cycles of the alternating current source, while the contacts of relay BCFR are maintained picked up during the remaining half cycles by the energy supplied from the condensers .BQ! and BQ2.

During the periods in which the CQIZIEQCR df'ule code transmitter CT governing the circuit of transformer BTT is open energy is not supplied over the rails of section BT to transformer BCTT and therefore is not supplied from this transformer to the windings of relay BCFR. However, the supply of current from transformer BLT to the circuits of the windings of relay BCFR continues. During the half-cycles in which termi nal NX is positive with respect to terminal BX current is supplied over the circuits traced above from the secondary winding of transformer BLT to the windings l and II. However, since at this time current is not supplied from transformer BCTT to the circuits of the windings of relay BCFR, current of substantially equal value is supplied from transformer BLT to each of the relay windings, and as the current supplied from transformer BLT to the windings of relay BCFR flows in opposite directions through the relay windings, no force is exerted to pick up the relay contacts.

During the half cycles in which terminal BX is positive with respect to terminal NX, the transformer BLT supplies to the circuits of the windings voltage impulses of a polarity such that the flow of current is blocked by the rectifiers.

Accordingly, during the open-periods of the contact of the code transmitter governing the circuit of the transformer BTT, the contacts of relay BCFR release and remain released. Similarly, during the closed periods of the contact of the code transmitter governing the circuit of the transformer BTT, the contacts of relay BCFR pick up and remainpicked up.

During the picked-up periods of the contacts of relay BCFR energy is supplied to the slow release relay BFSA, while during-the released periods of relay BCFR energy is supplied over a front contact of relay BFSA to slow release relay BBSA and its contact is picked up to interrupt the circuit of the red lamp R. and establish the circuit of the green lamp G of signal SB.

The equipment associated with section CT operates in substantially the same manner and a detailed explanation of its operationis unnecessary.

When a train moving in the normal direction of traffic enters section ET, the shunting effect of the wheels and axles of the vehicles forming the train substantially prevents the supply of energy to the transformer BCTT and thus prevents the supply of energy from this transformer to the relay BCFR. Accordingly, although energy continues to be supplied to transformer BLT, the relay BCFR releases and remains released so that energy is no longer supplied to relay BFSA and it releases to interrupt the c-ircult of the relay BBSA so that it-releases to interrupt the circuit of the green lamp G and to establish the circuit of the red lamp R of signal SB.

When section ET is vacated, energy from transformer BTT is again supplied over the section rails to transformer BCTT so that it supplies energy to relay- BCFR to cause the relay contacts to pick up. As a result of the code following operation of relay BCFR, the relays BFSA and BBSA are energized and the circuit of .the green lamp G of signal SB is established.

The relay BCFR and associated apparatus are arranged so that if the insulated joints 3 separating sections AT and BT are defective so that energy supplied from transformer ATT to the rails of section AT feeds to. the transformer BC'I'I', it will not cause improper operation of relay BCFR.

As is obvious from the drawings, the transformers ATT and BTT are oppositely connected with the track rails with the result that, when energy supplied from transformer BTT causes rail l to be positive with respect to rail 2, the energy supplied from transformer ATT causes rail '2 to be positive with respect to rail 1 and vice versa.

For purposes of illustration it will be assumed that the joints 3 separating sections AT and BT become defective as a result of passage of a train so that energy of normal relative polarity from transformer ATT feeds to the transformer BCTT at a time when the supply of energy of reverse relative polarity from transformer BTTto transformer BCTT is cut off because of occupancy of section BT.

Under these conditions, current continues to be supplied from transformer BLT to the circuits of the windings of the relay BCFR. During the half cycles in which terminal NX is positive with respect to terminal BX, the current supplied from transformer BLT to the circuits of both windings of relay BCFR is of the polarity effective to flow through the rectifiers included in these circuits.

In addition, during the half cycles when terininal NX is positive, and assuming the contact of the code transmitter CT governing the supply of energy to transformer ATT to be closed, energy from transformer ATT is supplied to transformer BCTT and causes to beinduced in each of the two portions of the transformer secondary winding an impulse of'voltag'e of the polarity in which the upper end of the winding portion is positive with respect to the lower end of the winding portion.

Accordingly, the voltage impulse induced in the upper portion 14 of the secondary Winding of transformer BCTT causes current to flow from the upper end terminal of the secondary winding through the rectifier Kl, through the upper winding ID of relay BCFR from right to left to terminal l6 and thence to terminal 12. The current supplied from the upper portion I4 of the secondary winding of transformer BCCT to the upper winding IQ of relay BCFR supplements or adds to that supplied to this winding from transformer BLT.

At this time, an impulse of voltage is supplied from the lower portion l5 of the secondary winding of transformer BCTT to the circuit of the winding H of relay BCFR and tends to cause current to flow from terminal 82 through the secondary winding of transformer BLT to ter minal [-6, and thence through the lower winding ll of relay BCFR from right to left but this current is blocked by the rectifier K2. Although the voltage supplied from portion of the secondary winding of transformer BCTT is prevented from causing the flow of current in the circuit of winding ll of relay BCFR by the rectifier K2, this voltage acts to reduce the effect of the voltage supplied from transformer BLT.

Accordingly, during the half cycle in which terminal NX is positive with respect to terminal BX the current supplied to the upper winding 10 of relay BCFR is due to the sum of the voltage impulses supplied to the circuit of this winding from the transformers BLT and BCTT, while that supplied to winding H of relay BCFR is due to the difference between the voltage impulses supplied to the circuit of this winding from the transformers BLT and BCTT, The current supplied to the windings l0 and II flows through the windings in opposite directions, but the current supplied to winding i 9 predominates. However, the current supplied to winding l9 fio'ws therethrough from right to'left and the relay BCFR is of a type the contacts of' whi'ch pick up only when current flows through the relay winding in the opposite direction so the relay contacts remain released.

During the half cyclesin which terminal BX is positive with respect to terminal NX, the'trafis; former BLT supplies voltage to the cir'cuits'of windings l and H of relay BCFR .of'a polarity such that the flow of current is blocked by the rectifiers KI and K2. p

In addition, during the half cycles in which terminal BX is positive withrespect to terminal NX, the energy supplied'from transformer ATT and feeding over the defectivejoi-nts to transformer BCTT induces in .each of the two pertions of the secondary winding of transformer BCTT a voltage of such polarity that the lower end of each winding portion is positive with respect to the upper end of the same winding por-v tion.

The voltage induced in the. lower portion l of the secondary winding of transformer BCTT tends to cause current to flow from the lower end terminal of this winding through therectifier K2 and through the lower winding ll of relay BCFR but this current is prevented from flowing by the presence of the opposing voltage of greater value supplied to this circuit from transformer BLT. a

The voltage induced in the upper portion M of transformer BCTT tends to cause current .to how from terminal 12 through the secondary winding of transformer BLT to terminal 16 and through the upper winding of .relay BCFR but this current is prevented from flowingloy the rectifier Kl. p

Accordingly, it is clear that during the, half cycles in which terminalBXlisgpositiye.withtrespect to terminal .NX, the .energysupplied over the defective joints from transformer to transformer BCTT cannot result in the :supply torelay BCFR .of energy effective to piclrupits contacts. o

It will be .seen, therefore, that under s the con: ditions stated, that is, that the insulated joints 3 separating sections AT and BT are defective so that energy from .transformerATT feeds to transformer. BCTT, the energy supplied from transformer ATT cannot cause to he suppliedito relay :BCFR energy effectivetopick up, its con tacts. Accordingly,.-if section -BT isoccupiedso that energy from, transformer B'I'I is not sup:- plied to transformer BCTT, .therelay-VBCFR-is certain :to remainwreleased so that relays rBE-SA and BBSA remain released jand-;,cause the red or stop lamp R of signal SBto}, be; lighted. p

:In like manner the transformers-JB'IEIand are "oppositely connected :with the rails ,of the track stretch, whilethe transformer LCLT.1s.con-. nected with the, circuit of'theitransformenCCTe'I and the windings of relay CCFR in such manner that relay CCFR will be'effectively" energized only when the energy supplied over the track rails is of the same relative polarity as' that supplied from transformer 'C'I' I" and iiwilfnot" be effectively energized when the energyisufpplied over the track rails is of the relative polarity opposite to that supplied from transformer B'I'I. This insures that relay CCFR will not heoper ated by energylsupp'lied from transfor iier BTT in the event theinsulated joint's separating seetions 28']? and GT are defective and thus insures that signal SC will not improperly" display a permissive indication at such times. "The equipment is also arranged so that failure of the supplyof energy to a line transformer, such as" transformer BLT, cannot result'in im proper operation of the associated track relay. If energy ceases to be supplied to transformer BLT, this transformer will cease to supply energy to'the circuits of the windings of relay BCFR. if transformer B'ITcontinues'to supply energy to transformer BCTT, current will continue to be supplied therefrom to the windings of relay BCFR. During half of the time the voltage in duced inthe't'wo portions of the secondary winding of transformer BCTT is of the polarity in which the upper' end terminal of the winding portion is positive with respect to the lower end terminal of the same Winding portion. At this time, therefore, current from the upper portion M of .the secondary winding of transformer BCTT flows through rectifier. KI and upper winding ll) of relay BCFR from right to left, and thence through the secondary winding of transformer BLTlto terminal 12. At this time current from the lower portion I5 of the secondary ,winding of transformer BLT tends to flow through the lower winding Ll of relay BCFR but is blocked by the rectifier K2.

In similar manner, during the remaining half of the time the voltages induced in the two portions of thesecondary Winding of transformer BCTT are of the polarity in'which the lower end terminal of reach winding portion is positive with respect to the upper end terminal of the same winding portion. At this time, therefore, current induced in the lower portion l5 of the secondary winding of transformer BCTT-flows through rectifier K2 and through the lower winding ll of relay BCFR from left to right and thence through the secondary winding of transformer BLTto terminal l2. The voltage induced in the upper portion l4 .of the secondary winding of transformer BCTT tends to cause current to flow from terminal l2 through the secondary winding of transformer BLT and thence through the upperowinding ID of relay BCFR but it is blocked by the rectifier Kl. f

It will .be seen that, after energy ceases to be supplied from transformer BLT, the windings l0 and H of relay'BCER are alternately energized Ifrom' transformer BCTT, and that the current-suppliedto the two windings of relay BCFR flows through one windingin one direction and through the other winding in the other direction so that they develop fiux of opposite polarity in the relay core. The relayBCFR. will only respond to energy of the polarity supplied to the lower winding and the impulses of energy supplied to this jwindingiwhen' offset by'opposing impulsessupplied to the winding it) 'are ineffective to pick up the relay contacts. .Hence, the relay contacts remainjreleasedl and relays BFSA and BBSA are'jrele'ased and hold signal S3 at o The equipment is also arranged so that failure ofeither or'both of the rectifiers KI and K2 cannot result in improper; Operation of relay BCF'R If rectifier Kl breaks down and permits cur.

transformer BLT during both half cycles of the alternating current source. In the half cycles in which terminal BX is positive with respect to terminal NX, current from the secondary winding of transformer BLT flows to terminal 16, through the upper winding [0 of relay BCFR from left to right, through rectifier KI, which is assumed to be defective, and through the upper portion [4 of thesecondary winding of transformer BCTT to the other terminal of the secondary winding of transformer BLT. At this time flow of current from the secondary winding of transformer BLTthrough winding H of relay BCFR is blocked by rectifier K2.

During the half cycles in which terminal. BX is positive with respect to terminal NX, the energy supplied from transformer BT to transformer BCTT causes .voltageto be induced in both portions of the. transformer secondary winding, this voltage being of the polarity in which the upper end terminal of each winding portion is positive with respect to the lower end terminal of the same winding portion. The voltage from the upper portion I l is supplied to the circuit of the upper winding H) of relay BCFR and opposes the voltage supplied at this time from transformer BLT. As explained above, the volta e from transformer BLT is of greater value than that from winding portion [4, so the voltage from transformer BCTT reduces but does not co'mpletelyprevent the supply of current from transformer BLT through winding In of relay BCFR. The voltage induced in the lower portion 15 of the secondary winding of transformer BCTT tends to cause current to flow through the winding H of relay BCFR but is blocked by rectifier K2. During this half cycle,

therefore, the winding [0 of relay BCFR is energized from left to right by current due to the difference between the voltages of the impulses supplied from transformer BLT and from portion M of the secondar'ywinding of transformer BCTT.

During the other half cycles, that when terminal NX is positive with respect to terminal BX, the transformer'BLT supplies to the circuits of both of the windings of relay BCFR voltage of the polarity effective to cause current to flow through the rectifiers, and the current supplied to winding flows therethrough from right to left and the current supplied to winding ll flows therethrough from left to right.

During these half cycles the energy supplied over the track rails from transformer BTT to transformer BCTT causes to be induced in both portions of the secondary winding of transformer BC'I'I an impulse of voltage of the polarity in which the lower end terminal of the winding portion is positive with respect to the upper end terminal of the same winding portion.

The current induced in lower portion l5 of the secondary winding of transformer BCT'I is supplied to winding ll of relay BCFR and supplements that supplied at this time from transformer BLT. The voltage induced in the upper portion M of the secondary winding of transformer BCIT tends to cause current to flow from terminal 12 through the secondary winding of transformer BLT and theme from left to right through the winding in of relay BCFR, butthis voltage is opposed by voltage of the opposite polarity and of greater value supplied at this time from transformer BLT.

Accordingly, after rectifier Kl breaks down, the relay BCFR will be energized substantially the same as normally, except for the supply to 12 winding ID of current of the polarity eifective to pick up the relay contacts.

During the open periods of the contact of the code transmitter CT governing the circuit of transformer BTI, energy will not be supplied over the track to transformer BCTT; At this time energy continues to be supplied from transformer BLT, and during the half cycles in which terminal NX is positive with respect to terminal BX voltage is supplied from transformer BLT to both windings of relay BCFR and currents flow through them in opposite directions so that they oifset each other. During the half cycles in which terminal BX is positive with respect to terminal NX, voltage from transformer BLT is supplied to the circuits of both windings of the relay but current is prevented from flowin in Winding H by the rectifier K2. As rectifier. Kl is assumed to be defective current from transformer BLT flows through the upper winding ID of relay BCFR from left to right, and, therefore, is of the polarity effective to pick up the contacts of relay BCFR or to hold them picked up if they are already picked up. If the current supplied to the winding I0 is of such value as to prevent release of relay BCFR, the relay contacts will remain continuously picked up and relay BBSA will release to cause signal SB to display its red or stop indication.

The equipment operates in substantially the same manner if the supply of energy to transformerBCTT is out off because of occupancy of section BT instead of because of interruption of the supply of energy to transformer BTT. If, during occupancy of section ET, the current supplied from transformer BLT to relay BCFR through the defective rectifier Kl picks up the contacts of relay BCFR, the relay contacts will be steadily picked up and relay BBSA will remain released and maintain the display of the stop indication by signal SB.

If the rectifiers KI and K2 both become defective, alternating current from transformer BLT will flow in the windings of relay BCFR, the current in one winding offsetting that in the other winding so no force is exerted to pick up the relay contacts. The voltage supplied from transformer BCTT to the circuits of the windings of relay BCFR is of the polarity such that it tends to cause current to flow in the same direction through both of the relay windings, the direction of flow being from left to right during alternate half cycles of the alternating current source and being from right to left during the other half cycles. Accordingly, the current from transformer BCTT alternately increases and decreases the force exerted tending to pick up the relay contacts. The relay BCFR, although of a type the contacts of which are quick to respond, will not respond to impulses of the duration of one half a cycle of the source so the relay contacts remain released. As the contacts of relay BCFR remain released the relays BESA and BBSA are released and signal SB remains at stop.

Modification shown in Fig. 2

In Fig. 2 of the drawings there is shown a'modification which may be employed in place of that shown in Fig. 1 when the code following relay is provided with a single winding. As shown, resistors A and I IA are connected in series across the terminals of the winding of relay BCFRA, while the left-hand end terminal of the secondaly. winding of transformer BLT is connected to terminal IDA intermediate the resistors IDA and "The resistors IDA and HA thus .constitute two load or supply circuits for the relay which replace thewindings ID and II, and in Fig 2; the transformers BCTT and BLT supply to the circuits of the. resistors IDA and IIA currents of a polarity and value substantially equivalent to that supplied. to the corresponding windings of relay BCFR of the species shown in Fig. 1. As the resistors IDA and HA are connected in series, the resultant voltage across the resistors is proportional to the difierence between the opposing currents supplied to the resistors individually, and as the winding of relay BCFRA is connected multiple-with the resistors IDA and HA, the current supplied to the winding of relay BCFRA is proportional to the difierence in the two currents supplied to the resistors IDA and HA. 1

' As explained in connection With Fig. 1, when the energy supplied over the track rails to transformer. BCTT and that supplied from transformer BLThas the proper phase relationship, and terminal NX of the source is positive with respect to terminal BX, the voltage supplied to the circuit of resistor I IA is the sum of the Voltage impulses supplied from transformers BLT and BCTT and is of the polarity in which the lower end terminal of the resistor IIA is positive with respect toterminal IDA. At this time resistor IDA is supplied with voltage of the polarity in which its upper end terminal is positive with respect to terminal IDA and of the magnitude determined by the difference between the voltages supplied from transformers BLT and BCTTV As a result the voltage supplied to resistor IDA in part offsets that supplied to resistor IIA, but there 'is'a resultant voltage across the resistors and the winding of relay BCFRA which is of the polarity such that current flows through the winding of relay BCFRA from left to right. This current is eifective to pick up the contacts of relay BCFRA, while the resistors IDA and IIA snub the relay BCFRA to prevent release of its contacts during the'half cycles in which terminal BX is positive with respect to terminal NX. I

This modification operates in substantially the same manner as that-shown in Fig. lwhen-the supply of energy over the track rails to transformer BCTT is cut ofi? or when energy of the wrong relative polarity is supplied thereto, or in the event one or both of the rectifiers or resistors is defective, and a detailed description of the operation of the equipment at such times is unnecessary.

Modification shown in Fig. 3

The modification shown in Fig 3 of the drawings is similar to that shown in-Fig. 1 but differs therefrom in that the condensers employed in Fig. 1 are replaced by rectifiers or asymmetric units K3 and K4 which are poled to permit fiow of energy of the polarity supplied from terminal I6 and to prevent flow of energy in the opposite direction.

The operation of this species is similar to that shown in Fig. 1 except that the rectifiers K3 and K4 serve in place of condensers BQI and BQ2 to snub the windings of the relay BCFR to prevent release of the relay contacts during the half cycles in which the relay windings are not effectively energized. The operation of this species is otherwise substantially the same as that shown in Fig. 1 and a detailed explanation of its operation is not necessary.

my invention, what I are divided into insulated track sections including a rear section and a forwardsection, the-entrance end of said forward section fadjciningthe exit end of said rear section, a coded track circuit system for said stretch comprising, in comb'ina I ticn, a source of alternating current, means for each section for supplying coded alternating cur rent from said source to the rails at the exltend of such section, so arranged that the current supplied to the rails of adjoining sections is opposite in phase, a polarized relay for detecting oc'cu pancy of said forward section having a contact biased to it released position, a first and a'second supply circuitfor said relay each including a half wave rectifier for governing the operation of its contact, a track transformer having a primary winding connected across the rails at the entrance end of said forward section and a secondary winding having a first portion connected to said first supply circuit and a second portion connected to said second supply circuit, the rectifiers in said supply circuits being'so'p'oledthat'when alternating current is supplied to said primary winding the voltage induced thereby insai'dportions dur ing one half of each alternating current cycle tends to cause current totfiow 'ina first direction in the first supply circuit onlywhile during the other half of each cycle'it tends to cause current ofthe same value to now in the opposite direction inthe second supply circuit only,'phase discriminating means which locally superimposes a voltage of constant 'efiective value derived from i said alternating current sourceon both said supply circuits, said superimposed voltage being higher in value than said induced voltage and of such phase "that when the induced voltage is due to current supplied at the exit end of the same section the local and induced voltages are additive in said "first supply circuit and in opposition in said second supply circuit, theresultant volt,- age being efiective duringsaid one'half only of each cycle to cause pulsating currentto ffiowi in saidfirst' direction insaid first supply circuit. and

in the opposite direction in said second'supply circuit, means comprising said supply circuits for causing the relay contact toassume its pickede up position when and only When the pulsating current in said first supplycircuit exceeds the opposing current in said second supply circuit, and code detecting means governed by said contact.

2. In a coded railway signaling system, a coded track system of the type recited in claim 1, in

which the phase discriminating means comprises a line transformer which has a primary Winding supplied locally with alternating current and a secondary winding connected to both of the relay supply circuits and adapted to supply sumcient voltage thereto to block the flow of pulsating current in either supply circuit during one half of each alternating current cycle irrespective of the relative polarity of the voltage supplied thereto by the associated track transformer, and to cause the flow of pulsating current in said first direction in the first supply circuitand in the opposite direction in the second supply circuit during the other half of each alternating current cycle.

3. In a coded railway signaling system, a coded track circuit system of the type recited in claim 1, in which the phase discriminating means comprises a line transformer which has a primary winding supplied locally with alternating current and-a secondarywinding connected to both of the relay supply circuits and adapted-to supply sufiicient voltage thereto to block the flow of pulsating current in either supply circuit during one half of each alternating current cycle and to cause the flow of pulsating current in said first direction in the first supply circuit and in the opposite direction in the second supply circuit during the other half of each alternating current cycle, said track transformer being efiective to increase the pulsating currentin the first supply ,circuit and to decrease that in the second it supplied with alternating currentof one relative polarity, and to decrease the pulsating current in the first supply circuit and to increase that in the second if supplied wilh alternating current of the opposite relative polarity.

4. In a coded railway signaling system, a coded track circuit system of the type recited in claim 1, in which the polarized relay isof the differential type and has two windings'one of which is connected in series in said first supply circuit in such manner that current flowing therein tends to cause the relay to move its contact to the picked-up position, and the other is connected in series with the second supply circuit in such manner that current flowing therein in said opposite direction tends to cause the relay to move its contact to the biased position, said relay also having a snubbing circuit for each winding eifective to prevent the vibration of said contact due to the pulsation of the currents in said supply circuits.

5. In a coded railway signaling system, a coded track circuit system of the type recited in claim 1, in which the polarized relay has a single winding which is connected in a bridge circuit across the end terminals of two series connected resistors through which pulsating currents flow in opposite directions, said resistors constituting the supply circuits for said relay,-said relay winding being connected in such manner that the relay tends to 'move its contact to the picked-up position when the pulsating current in the first supply circuit exceeds that in the second, and to move its contact to the biased position when the pulsating current in the second supply circuit exceeds that in the first, said resistors also providing a snubbing circuit for the relay winding effective to prevent-the vibration of said contact due to the pulsation of the currents in said supply circuits.

6. In combination, a, source of alternating current, a polarized relay having a contact movable between two positions, a first and a second supply circuit for said relay each including a half wave rectifier for governing the operation of its contact, a transformer having a primary winding supplied at times with alternating current from said source and a secondary winding having a first portion connected to said first supply circuit and a second portion connected to said second supply circuit, the rectifiers in said supply circuits'being so poled that when alternating current is supplied to said primary winding the voltage induced thereby in said portions during one half of each alternating current cycle tends to cause current to fiow in a first direction in the first supply circuit only while during the other half of each cycle it tends to cause current of the same value to flow in the opposite direction in the second supply circuit only, phase discriminating means for superimposing a voltage of constant effective value derived from said alternating current source on both said supply circuits, said superimposed voltage being higher in value than said induced voltage, said voltages being effective to cause pulsating current to flow in proportion to their sum in the first supply circuit and an opposing current to flow in proportion to their difference in the second supply circuit during said one half only of each alternating current cycle provided the superimposed voltage is of a given relative polarity, said voltages being also effective to cause corresponding currents to flow in both circuits during the other half only of each alternating current cycle, in the event the superimposed voltage is of the opposite relative polarity, in which case the pulsating current in the first supply circuit is correspondingly less than that in the second, and means for effectively energizing said relay in proportion-to the difference in the currents in said first and second supply circuits, so arranged as to cause the relay to move its contact in one direction when the pulsating current in .the first supply circuit is the greater and in the other direction when the opposing current in the second supply circuit is the greater as determined by the relative polarity of the voltage supplied by said phase discriminating means.

DOUGLAS GOLDIE SHIPP.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,781,827 Thompson Nov. 18, 1930 1,824,119 Carter Sept. 22, 1931 2,243,740 OI-Iagen May 27, 1941 

